Without going too far into metadata, file format etc (as I don't know a lot about these) is it worth trying different profiles if a video won't play?I have a Panasonic DMP BD77 and find neither the General profile and Panasonic BD profile will work on some files.But if convert these with Handbrake they plays OK., but it would be nice to not need to do that.

You can't hurt anything trying different profiles. The DirecTV profile transcodes everything, while the Generic profile does nothing. Everything else has some level of transcoding. I rarely use the DLNA player in my Panasonic TV anymore, as it just isn't that great of an interface. I usually use a Roku player. Without knowing more about the videos that won't play (container and codecs) there isn't much more I can say.